1. Field of the Invention
This invention relates to a novel ultrafine fiber entangled sheet and a method for the production thereof. More particularly, the present invention relates to a novel entangled non-woven fabric having a fiber structure which includes a layer comprised of ultrafine fiber bundles that are entangled with one another and a layer comprised of ultrafine fibers to fine bundles of ultrafine fibers wherein both layers are nonuniformly distributed in the direction of fabric thickness, and to a method of producing the entangled non-woven fabric. Further, the present invention relates to a novel grained sheet having a grain composed of densely entangled ultrafine fibers to fine bundles of the ultrafine fibers and resin and to a method of producing the novel grained sheet.
2. Description of the Prior Art
Typical examples of conventional non-woven fabrics include (1) non-woven fabric which is produced by webbing conventional staple fibers into a random web and then needle-punching the web, and (2) non-woven fabric as disclosed in Japanese Patent Publication No. 24699/1969 which has a fiber structure which consists principally of single fibers that are gathered and bundled, and in which the fiber bundles are entangled with one another while maintaining the bundle form. However, since fabric (1) has a fiber structure which is relatively thick and the fibers are individually three-dimensionally entangled with one another, the non-woven fabric has low flexibility and very poor tactile properties. Hence, the commercial value of this non-woven fabric has been considerably limited. Although fabric (2) has higher flexibility than fabric (1), non-woven fabric (2) has extremely low shape retention.
With regard to grained sheets, the grain of conventional synthetic leather consists of a porous or nonporous layer of resin, such as polyurethane elastomer, or of an integral laminate of the porous layer with the nonporous layer. However, synthetic leather having such a grain has various drawbacks such as low feel of integration, a very undesirable rubber-like feel, low crumple resistance, excessively uniform and shallow surface luster, and so forth.
To eliminate these drawbacks, various proposals have been made. These proposals include:
(1) Various fillers, such as fine particles, are added in forming the grain.
(2) Ultrafine fibers are arranged along the surface and combined with a porous material to form the grain. (Japanese Patent Publication No. 40921/1974).
(3) A surface fluff fiber and resin are combined to form the grain.
(4) The surface fibers are melted or dissolved so as to locally bond the fibers and form the grain.
However, method (1) has drawbacks in that the flexibility is reduced and the grain luster of the product is diminished by addition of the filters. Since the product obtained by method (2) has a grain fiber structure in which the ultrafine fibers are arranged along the surface in bundle form, the surface fluffs and peeling develops along the surface of the arrangement of the fiber bundles to cause "loose grain" if the sheet or leather is strongly crumpled or shearing stress is repeatedly applied to the sheet. Where the crumpling, or repeated shearing stress continues, cracks eventually occur on the surface. Moreover, fine unevenness occurs on the surface along the bundles of the ultrafine fibers and degrades the surface appearance. The products obtained by methods (3) or (4) have drawbacks in that the surface cracks relatively easily, severely degrading the appearance, when the sheet is repeatedly bent or shearing stress is repeatedly applied to the sheet.